package com.github.kezhenxu94.playground.java.atoffer;

/**
 * 重建二叉树
 * 
 * 输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。
 * 假设输入的前序遍历和中序遍历的结果中都不含重复的数字。
 * 例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}， 则重建二叉树并返回。
 * 
 * @author Ke Zhenxu
 *
 */
public class AtOfferReconstructTree {
	
	public static void main(String[] args) {
		AtOfferReconstructTree sol = new AtOfferReconstructTree();
		System.out.println(sol.reConstructBinaryTree(new int[] {1,2,3,4,5,6,7}, new int[] {3,2,4,1,6,5,7}));
	}

	public TreeNode reConstructBinaryTree(int[] pre, int[] in) {
		return buildTree(pre, 0, pre.length - 1, in, 0, in.length - 1);
	}
	
	private TreeNode buildTree(int[] pre, int preFrom, int preTo, int[] in, int inFrom, int inTo) {
		if (preTo < preFrom || inTo < inFrom)
			return null;
		TreeNode root = new TreeNode(pre[preFrom]);
		if (preTo == preFrom || inTo == inFrom)
			return root;
		
		int leftCount = 0;
		for (int i = inFrom; i <= inTo && in[i] != root.val; i++)
			leftCount++;
		
		root.left = buildTree(pre, preFrom + 1, preFrom + leftCount, in, inFrom, inFrom + leftCount - 1);
		root.right = buildTree(pre, preFrom + 1 + leftCount, preTo, in, inFrom + leftCount + 1, inTo);
		return root;
	}
}
